Message-ID: <CADhLXY7+rJwz=AnZ_GYAZZuKn_5_KMSkSx5_aYuiqcO58ZiLtA@mail.gmail.com>
Date: Fri, 28 Nov 2025 11:35:05 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: Heming Zhao <heming.zhao@...e.com>, mark@...heh.com, jlbec@...lplan.org, 
	joseph.qi@...ux.alibaba.com
Cc: ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	syzbot+ab0ad25088673470d2d9@...kaller.appspotmail.com
Subject: Re: [PATCH v4] ocfs2: validate inline xattr size and entry count in ocfs2_xattr_ibody_list

On Thu, Nov 20, 2025 at 12:19 PM Heming Zhao <heming.zhao@...e.com> wrote:
>
> On Thu, Nov 20, 2025 at 09:41:45AM +0530, Deepanshu Kartikey wrote:
> > Add comprehensive validation of inline xattr metadata in
> > ocfs2_xattr_ibody_list() to prevent out-of-bounds access and
> > use-after-free bugs when processing corrupted inline xattrs.
> >
> > The patch adds two critical validations:
> >
> > 1. Validates i_xattr_inline_size before use:
> >    - Ensures it does not exceed block size
> >    - Ensures it is at least large enough for xattr header
> >    - Prevents pointer arithmetic with corrupted size values that could
> >      point outside the inode block
> >
> > 2. Validates xattr entry count (xh_count):
> >    - Calculates maximum entries that can fit in the inline space
> >    - Rejects counts that exceed this limit
> >    - Prevents out-of-bounds array access in subsequent code
> >
> > Without these checks, a corrupted filesystem with invalid inline xattr
> > metadata can cause the code to access memory beyond the allocated space.
> > For example:
> > - A corrupted i_xattr_inline_size of 0 would cause header pointer
> >   calculation to point past the end of the block
> > - A corrupted xh_count of 22 with inline_size of 256 would cause
> >   array access 7 entries beyond the 15 that actually fit (the syzbot
> >   reproducer used xh_count of 20041), leading to use-after-free when
> >   accessing freed memory pages
> >
> > The validation uses the correct inline_size (from di->i_xattr_inline_size)
> > rather than block size, ensuring accurate bounds checking for inline
> > xattrs specifically.
> >
> > Reported-by: syzbot+ab0ad25088673470d2d9@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=ab0ad25088673470d2d9
> > Tested-by: syzbot+ab0ad25088673470d2d9@...kaller.appspotmail.com
> > Suggested-by: Heming Zhao <heming.zhao@...e.com>
> > Link: https://lore.kernel.org/all/20251111073831.2027072-1-kartikey406@gmail.com/ [v1]
> > Link: https://lore.kernel.org/all/20251117063217.5690-1-kartikey406@gmail.com/ [v2]
> > Link: https://lore.kernel.org/all/20251117114224.12948-1-kartikey406@gmail.com/ [v3]
> > Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
>
> LGTM
> Reviewed-by: Heming Zhao <heming.zhao@...e.com>
>
> > ---
> > Changes in v4:
> >  - Corrected commit message example: max entries is 15, not 7
> >    (pointed out by Heming Zhao)
> >
> > Changes in v3:
> >  - Moved validation from ocfs2_xattr_list_entries() to
> >    ocfs2_xattr_ibody_list() to use correct inline size calculation
> >    (suggested by Heming Zhao)
> >  - Added validation of i_xattr_inline_size before use
> >  - Added validation of xattr entry count against inline space
> >  - Changed return value to -EFSCORRUPTED for consistency
> > ---
> >  fs/ocfs2/xattr.c | 30 ++++++++++++++++++++++++++++--
> >  1 file changed, 28 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> > index d70a20d29e3e..98fd4f3f2d2d 100644
> > --- a/fs/ocfs2/xattr.c
> > +++ b/fs/ocfs2/xattr.c
> > @@ -971,13 +971,39 @@ static int ocfs2_xattr_ibody_list(struct inode *inode,
> >       struct ocfs2_xattr_header *header = NULL;
> >       struct ocfs2_inode_info *oi = OCFS2_I(inode);
> >       int ret = 0;
> > +     u16 xattr_count;
> > +     size_t max_entries;
> > +     u16 inline_size;
> >
> >       if (!(oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL))
> >               return ret;
> >
> > +     inline_size = le16_to_cpu(di->i_xattr_inline_size);
> > +
> > +     /* Validate inline size is reasonable */
> > +     if (inline_size > inode->i_sb->s_blocksize ||
> > +         inline_size < sizeof(struct ocfs2_xattr_header)) {
> > +             ocfs2_error(inode->i_sb,
> > +                         "Invalid xattr inline size %u in inode %llu\n",
> > +                         inline_size,
> > +                         (unsigned long long)OCFS2_I(inode)->ip_blkno);
> > +             return -EFSCORRUPTED;
> > +     }
> > +
> >       header = (struct ocfs2_xattr_header *)
> > -              ((void *)di + inode->i_sb->s_blocksize -
> > -              le16_to_cpu(di->i_xattr_inline_size));
> > +              ((void *)di + inode->i_sb->s_blocksize - inline_size);
> > +
> > +     xattr_count = le16_to_cpu(header->xh_count);
> > +     max_entries = (inline_size - sizeof(struct ocfs2_xattr_header)) /
> > +                    sizeof(struct ocfs2_xattr_entry);
> > +
> > +     if (xattr_count > max_entries) {
> > +             ocfs2_error(inode->i_sb,
> > +                         "xattr entry count %u exceeds maximum %zu in inode %llu\n",
> > +                         xattr_count, max_entries,
> > +                         (unsigned long long)OCFS2_I(inode)->ip_blkno);
> > +             return -EFSCORRUPTED;
> > +     }
> >
> >       ret = ocfs2_xattr_list_entries(inode, header, buffer, buffer_size);
> >
> > --
> > 2.43.0
> >




Hi Joseph, Mark, Joel,

Gentle ping on this patch. It has been reviewed and approved by Heming:

  Reviewed-by: Heming Zhao <heming.zhao@...e.com>

This patch fixes a syzbot-reported use-after-free bug in OCFS2 inline
xattr handling. The fix adds validation of i_xattr_inline_size and
xh_count before use to prevent out-of-bounds access.

Should I resend with the Reviewed-by tag included, or is there anything
else needed for this to be picked up?

Thanks,
Deepanshu

Link: https://lore.kernel.org/all/20251120041145.33176-1-kartikey406@gmail.com/T/
[v4]

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